Manufacturing Process for Matrix Drill Bits

ABSTRACT

A process for reducing inclusions during manufacturing of a matrix drill bit comprises placing at least a first layer of a first matrix material in a matrix bit body mold. At least a second layer of a second matrix material is placed in the mold. A binder material is placed in the mold with the binder material disposed proximate the second layer of matrix material and a metal a blank. A graphite lid is placed on the mold. The mold and the materials disposed therein are heated to a selected temperature to cause the binder material to melt and to allow the hot, liquid binder material to infiltrate the second matrix material and the first matrix material, with the second matrix material operable to improve infiltration of the first matrix material by the hot, liquid binder material without using a flux material.

TECHNICAL FIELD

The present invention is related to rotary drill bits and moreparticularly to matrix drill bits having a composite matrix bit body.

BACKGROUND OF THE INVENTION

Rotary drill hits are frequently used to drill oil and gas wells,geothermal wells and water wells. Rotary drill bits may be generallyclassified as rotary cone or roller cone drill bits and fixed cutterdrilling equipment, or drag bits. Fixed cutter drill bits or drag bitsare often formed with a matrix bit body having cutting elements orinserts disposed at select locations of exterior portions of the matrixbit body. Fluid flow passageways are typically formed in the matrix bitbody to allow communication of drilling fluids from associated surfacedrilling equipment through a drill string. or drill pipe attached to thematrix bit body. Such fixed cutter drill bits or drag hits may sometimesbe referred to as “matrix drill bits.”

Matrix drill bits are typically formed by placing, loose matrix material(sometimes referred to as “matrix powder” into a mold and infiltratingthe matrix material with a binder such as a copper alloy. it is commonpractice to place a flux material over the infiltrant binder to helpremove gases such as oxygen or hydrogen or prevent their absorption intothe molten material. However, some infiltration defects may beattributed to the use of flux, for example, nonmetallic inclusions,impurities, and oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present embodimentsand advantages thereof may be acquired by referring to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features, and wherein:

FIG. 1 is a schematic drawing showing an isometric view of a fixedcutter drill bit having a matrix bit body formed in accordance withteachings of the present disclosure;

FIG. 2 is a schematic drawing in section with portions broken awayshowing one example of a mold assembly with a first matrix material anda second matrix material satisfactory for forming a matrix drill bit inaccordance with teachings of the present disclosure;

FIG. 3 is a schematic drawing in section with portions broken awayshowing a matrix bit body removed from the mold of FIG. 2 after bindermaterial has infiltrated the first matrix material and the second matrixmaterial;

FIG. 4 is a schematic drawing in section showing interior portions ofone example of a mold satisfactory for use in forming a matrix bit bodyin accordance with teachings of the present disclosure;

FIG. 5A is a schematic drawing showing a cross sectioned example of abinder sample manufactured without flux;

FIG. 5B is a schematic drawing showing a cross sectioned example of ahinder sample manufactured with flux; and

FIGS. 6A-6C show the metallographic defects for binder test samples withincreasing amounts of flux.

DETAILED DESCRIPTION OF THE DISCLOSURE

The terms “matrix drill bit” and “matrix drill bits” may be used in thisapplication to refer to “rotary drag bits”, “drag bits”, “fixed cutterdrill bits” or any other drill hit incorporating teaching of the presentdisclosure. Such drill bits may be used to form well bores or boreholesin subterranean formations.

Matrix drill bits are typically formed by placing loose matrix material(sometimes referred to as “matrix powder” into a mold and infiltratingthe matrix material with a binder such as a copper alloy. The mold maybe formed by milling a block of material, such as graphite to define amold cavity with features that correspond generally with desiredexterior features of the resulting matrix drill bit. Various features ofthe resulting matrix drill bit such as blades, cutter pockets, and/orfluid flow passageways may be provided by shaping the mold cavity and/orby positioning temporary displacement material within interior portionsof the mold cavity. A preformed steel shank or bit blank may be placedwithin the mold cavity to provide reinforcement for the matrix bit bodyand to allow attachment of the resulting matrix drill bit with a drillstring.

A quantity of matrix material typically in powder form may then beplaced within the mold cavity. The matrix material may be infiltratedwith a molten metal alloy or binder which will form a matrix bit bodyafter solidification of the binder with the matrix material. Tungstencarbide powder is often used to form conventional matrix bit bodies. Aflux material may be in contact with the melted material in an effort tominimize oxidation and remove non-metallic impurities in the liquidmelt.

In one embodiment, matrix drill bits may comprise a matrix bit bodyformed in part by at least a first matrix material and a second matrixmaterial. Such matrix drill bits may he described as having a compositematrix bit body since at least two different matrix materials withdifferent performance characteristics may be used to form the hit body.As discussed later in more detail, more than two matrix materials may heused to form a matrix bit body.

For some applications the first matrix material may have increasedtoughness or high resistance to fracture and also provide desirederosion, abrasion and wear resistance. The second matrix materialpreferably has only a limited amount (if any) of alloy materials orother contaminates. The first matrix material may include, but is notlimited to, cemented carbides or spherical carbides. The second matrixmaterial may include, but is not limited to, macrocrystalline tungstencarbides and/or cast carbides.

Various types of binder materials may be used to infiltrate matrixmaterials to form a matrix bit body. Binder materials may include, butare not limited to, copper (Cu), nickel (Ni), cobalt (Co), iron (Fe),molybdenum (Mo) individually or alloys based on these metals. Thealloying elements may include, but are not limited to, one or more ofthe following elements—manganese (Mn), nickel (Ni), tin (Sn) zinc (In),silicon (Si), molybdenum (Mo), tungsten (W), boron (B) and phosphorous(P). The matrix bit body may he attached to a metal shank. A tool jointhaving, a threaded connection operable to releasably engage theassociated matrix drill bit with a drill string, drill pipe, bottom holeassembly or downhole drilling motor may be attached to the metal shank.

The terms “cemented carbide” and “cemented carbides” may be used withinthis application to include WC, MoC, TiC, TaC, NbC, Cr₃C₂, VC and solidsolutions of mixed carbides such as WC—TiC, WC—TiC—TaC, WC—TiC—(Ta,Nb)Cin a metallic binder (matrix) phase. Typically, Co, Ni, Fe, Mo and/ortheir alloys may be used to form the metallic binder. Cemented carbidesmay sometimes he referred to as “composite” carbides or sinteredcarbides. Some cemented carbides may also be referred to as sphericalcarbides. However, cemented carbides may have many configurations andshapes other than spherical

Cemented carbides may be generally described as powdered refractorycarbides which have been united by compression and heat with bindermaterials such as powdered cobalt, iron, nickel, molybdenum and/or theiralloys. Cemented carbides may also be sintered, crushed, screened and/orfurther processed as appropriate. Cemented carbide pellets may be usedto form a matrix bit body. The binder material provides ductility andtoughness which often results in greater resistance to fracture(toughness) of cemented carbide pellets, spheres or other configurationsas compared to cast carbides, macrocrystalline tungsten carbide and/orformulates thereof.

The binder materials used to form cemented carbides may sometimes bereferred to as “bonding materials” in this patent application to helpdistinguish between binder materials used to form cemented carbides andbinder materials used to form a matrix drill bit.

As discussed later in more detail, metallic elements and/or their alloysin bonding materials associated with cemented carbides may “contaminate”hot, liquid (molten) infiltrants such as copper based alloys and othertypes of binder materials associated with forming matrix drill bits asthe molten infiltrant travels through the cemented carbides prior tosolidifying to form a desired matrix. This kind of “contamination”(enrichment of infiltrant with bonding material from cemented carbides)of a molten infiltrant may alter the solidus (temperature below whichinfiltrant is all solid) and liquid US temperature above whichinfiltrant is all liquid) of the infiltrant as it travels under theinfluence of capillary action through the cemented carbide. Thisphenomena may have an adverse effect on the wettability of the cementedcarbides resulting in lack of satisfactory infiltration of the cementedcarbides prior to solidifying to form the desired matrix.

Cast carbides may generally be described as having two phases, tungstenmonocarbide and ditungsten carbide. Cast carbides often havecharacteristics such as hardness, wettability and response tocontaminated hot, liquid binders which are different from cementedcarbides or spherical carbides.

Macrocrystalline tungsten carbide may he generally described asrelatively small particles (powders) of single crystals of monotungstencarbide with additions of cast carbide, Ni, Fe, Carbonyl of Fe, Ni, etc.Both. cemented carbides and macrocrystalline tungsten carbides aregenerally described as hard materials with high resistance to abrasion,erosion and wear. Macrocrystalline tungsten carbide may also havecharacteristics such as hardness, wettability and response tocontaminated hot, liquid binders which are different from cementedcarbides or spherical carbides.

The terms “binder” or “binder material” may be used in this applicationto include copper, cobalt, nickel, iron, any alloys of these elements orany other material satisfactory for use in forming a matrix drill bit.Such hinders generally provide desired ductility, toughness and thermalconductivity for an associated matrix drill bit. Other materials suchas, but not limited to, tungsten carbide have previously been used ashinder materials to provide resistance to erosion, abrasion and wear ofan associated matrix drill bit. Binder materials may cooperate with twoor more different types of matrix materials to form composite matrix bitbodies with increased toughness and wear properties as compared to manyconventional matrix bit bodies.

FIG. 1 is a schematic drawing showing one example of a matrix drill hitor fixed cutter drill bit formed with a composite matrix bit body. Forembodiments such as shown in FIG. 1, matrix drill bit 20 may includemetal shank 30 with composite matrix bit body 50 securely attachedthereto. Metal shank 30 may be described as having a generally hollow,cylindrical configuration defined in part by fluid flow passageway 32 inFIG. 3. Various types of threaded connections, such as AmericanPetroleum Institute (API) connection or threaded pin 34, may be formedon metal shank 30 opposite from composite matrix bit body 50.

For some applications, generally cylindrical metal blank or casting,blank 36 (See FIGS. 2 and 3) may be attached to hollow, generallycylindrical metal shank 30 using various techniques. For example annularweld groove 38 (See FIG. 3) may be formed between adjacent portions ofblank 36 and shank 30. Weld 39 may be formed in groove 38 between blank36 and shank 30. See FIG. 1. Fluid flow passageway or longitudinal bore32 preferably extends through metal shank 30 and metal blank 36. Metalblank 36 and metal shank 30 may be formed from various steel alloys orany other metal alloy associated with manufacturing rotary drill bits.

A matrix drill bit may include a plurality of cutting elements, inserts,cutter pockets, cutter blades, cutting structures, junk slots, and/orfluid flow paths that may be formed on or attached to exterior portionsof an associated bit body. For embodiments such as shown in FIGS. 1, 2and 3, a plurality of cutter blades 52 may form on the exterior ofcomposite matrix bit body 50. Cutter blades 52 may be spaced from eachother on the exterior of composite matrix bit body 50 to form fluid flowpaths or junk slots therebetween.

A plurality of nozzle openings 54 may be formed in composite bit body50. Respective nozzles 56 may be disposed in each nozzle opening 54. Forsome applications nozzles 56 may be described as “interchangeable”nozzles. Various types of drilling fluid may be pumped from surfacedrilling equipment (not expressly shown) through a drill string (notexpressly shown) attached with threaded connection 34 and fluid flowpassageways 32 to exit from one or more nozzles 56. The cuttings,downhole debris, formation fluids and/or drilling fluid may return tothe well surface through an annulus (not expressly shown) formed betweenexterior portions of the drill string and interior of an associated wellbore (not expressly shown)

A plurality of pockets or recesses 58 may be formed in blades 52 atselected locations. See FIG. 3. Respective cutting elements or inserts60 may be securely mounted in each pocket 58 to engage and removeadjacent portions of a downhole formation. Cutting elements 60 mayscrape and gouge formation materials from the bottom and sides of awellbore during rotation of matrix drill bit 20 by an attached drillstring. For some applications various types of polycrystalline diamondcompact (PDC) cutters may he satisfactorily used as inserts 60. A matrixdrill bit having such PDC cutters may sometimes be referred to as a “PDCbit”. It will be readily apparent to persons having ordinary skill inthe art that a wide variety of fixed cutter drill bits, drag bits andother drill bits may be satisfactorily formed with a composite matrixbit body incorporating teachings of the present disclosure. The presentdisclosure is not limited to matrix drill bit 20 or any specificfeatures as shown in FIGS. 1-4.

A wide variety of molds may be satisfactorily used to form a compositematrix bit body and associated matrix drill bit in accordance withteachings of the present disclosure. Mold assembly 100 as shown in FIGS.2 and 4 represents only one example of a mold assembly satisfactory foruse in forming a composite matrix bit body incorporating teachings ofthe present disclosure. U.S. Pat. No. 5,373,907 entitled Method AndApparatus For Manufacturing And Inspecting The Quality Of A Matrix BodyDrill Bit shows additional details concerning mold assemblies andconventional matrix bit bodies.

Mold assembly 100 as shown in FIGS. 2 and 4 may include severalcomponents such as mold 102, gauge ring or connector ring 110 and funnel120. Mold 102, gauge ring 110 and funnel 120 may be formed from graphiteor other suitable materials. Various techniques may be used including,but not limited to, machining a graphite blank to produce mold 102 withcavity 104 having a negative profile or a reverse profile of desiredexterior features for a resulting fixed cutter drill bit. For examplemold cavity 104 may have a negative profile which corresponds with theexterior profile or configuration of blades 52 and junk slots or fluidflow passageways formed therebetween as shown in FIG. 1.

As shown in FIG. 4, a plurality of mold inserts 106 may be placed withincavity 104 to form respective pockets 58 in blades 52. The location ofmold inserts 106 in cavity 104 corresponds with desired locations forinstalling cutting elements 60 in associated blades 52. Mold inserts 106may he formed from various types of material such as, but not limitedto, consolidated sand and graphite. Various techniques such as brazing,may be satisfactorily used to install cutting elements 60 in respectivepockets 58.

Various types of temporary displacement materials may be satisfactorilyinstalled, within mold cavity 104, depending upon the desiredconfiguration of a resulting matrix drill bit. Additional mold inserts(not expressly shown) formed from various materials such as consolidatedsand and/or graphite may be disposed within mold cavity 104. Variousresins may be satisfactorily used to form consolidated sand. Such moldinserts may have configurations corresponding with desired exteriorfeatures of composite bit body 50 such as fluid flow passageways formedbetween adjacent blades 52. As discussed later in more detail, a firstmatrix material having increased toughness or resistance to fracture maybe loaded into mold cavity 104 to form portions of an associatedcomposite matrix bit body that engage and remove downhole formationmaterials during drilling of a wellbore.

Composite matrix, bit body 50 may include a relatively large fluidcavity or chamber 32 with multiple fluid flow passageways 42 and 44extending therefrom. See FIG. 3. As shown in FIG. 2, displacementmaterials such as consolidated sand may be installed within moldassembly 100 at desired locations to form portions of cavity 32 andfluid flow passages 42 and 44 extending therefrom. Such displacementmaterials may have various configurations. The orientation andconfiguration of consolidated sand legs 142 and 144 may be selected tocorrespond with desired locations and configurations of associated fluidflow passageways 42 and 44 communicating from cavity 32 to respectivenozzle outlets 54. Fluid flow passageways 42 and 44 may receive threadedreceptacles (not expressly shown) for holding respective nozzles 56therein.

A relatively large, generally cylindrically shaped consolidated sandcore 150 may be placed on the legs 142 and 144. Core 150 and legs 142and 144 may be sometimes described as having the shape of a “crow'sfoot.” Core 150 may also be referred to as a “stalk.” The number of legsextending from core 150 will depend upon the desired number of nozzleopenings in a resulting composite hit body. Legs 142 and 144 and core150 may also be formed from graphite or other suitable material.

After desired displacement materials, including core 150 and legs 142and 144, have been installed within mold assembly 101), first matrixmaterial 131 having desired fracture resistance characteristics(toughness) and erosion, abrasion and wear resistance, may be placedwithin mold assembly 100. First matrix material 131 will preferably forma first zone or a first layer, which will correspond approximately withexterior portions of composite matrix bit body 50 that will contact andremove formation materials during drilling of a wellbore. The amount offirst matrix material 131 added to mold assembly 120 will preferably belimited such that matrix material 131 does not contact end 152 of core150. The present disclosure allows the use of matrix materials havingdesired characteristics of toughness and wear resistance for forming afix cutter drill bit or drag bit.

A generally hollow, cylindrical metal blank 36 may then be placed withinmold assembly 100. Metal blank 36 may comprise inside diameter 37 whichis larger than the outside diameter of sand core 150. Various fixtures(not expressly shown) may be used to position metal blank 36 within moldassembly 100 at a desired location spaced from first matrix material131.

Second matrix material 132 may then be loaded into mold assembly 100 tofill a void space or annulus formed between outside diameter 154 of sandcore 150 and inside diameter 37 of metal blank 36. Second matrixmaterial 132 preferably covers first matrix material 131 includingportions of first matrix material 131 located adjacent to and spacedfrom end 152 of core 150.

For some applications second matrix material 132 is preferably loaded ina manner that eliminates or minimizes exposure of second matrix material132 to exterior portions of composite matrix bit body 50. First matrixmaterial 131 may be primarily used to form exterior portions ofcomposite matrix bit body 50 associated with cutting, gouging andscraping downhole formation materials during rotation of matrix drillbit 20 to form a wellbore. Second matrix material 132 may be primarilyused to form interior portions and exterior portions of composite matrixbit body 50 which are not normally associated cutting, gouging andscraping downhole formation materials. See FIGS. 2 and 3.

For some applications third matrix material 133 such as tungsten powdermay then be placed within mold. assembly 100 between outside diameter 40of metal blank 36 and inside diameter 122 of funnel 120. Third matrixmaterial 133 may be a relatively soft powder which forms a matrix thatmay, subsequently, be machined to provide a desired exteriorconfiguration and transition between matrix bit body 50 and metal shank36. Third matrix 133 may sometimes be described as an “infiltratedmachinable powder” Third matrix material 133 may be loaded to cover all,or substantially all, of second matrix material 132 located proximateouter portions of composite matrix bit body 50. See FIGS. 2 and 3.

During the loading of matrix material 131, 132 and 133, care should betaken to prevent undesired mixing between first matrix material 131 andsecond matrix material 132, and undesired mixing between second matrixmaterial 132 and third matrix material 133. Slight mixing at theinterlaces to avoid sharp boundaries between different matrix materialsmay provide smooth transitions for bonding between adjacent layers.Prior experience and testing has demonstrated various problemsassociated with infiltrating cemented carbides and spherical carbideswith hot, liquid binder material when the cemented carbides andspherical carbides are disposed in relatively complex mold assembliesassociated with matrix, bit bodies for fixed cutter drill bits. Similarproblems have been noted when attempting to form matrix bodies withcemented carbides and/or spherical carbides for other types of complexdownhole tools associated with drilling and producing oil and gas wells.

Manufacturing problems and resulting quality problems associated withusing cemented carbides and/or spherical carbides as matrix material aregenerally associated with lack of infiltration, porosity, shrinkage,cracking and segregation of binder material constituents within interiorportions of a resulting matrix bit body. Relatively complicated,intricate designs and relatively large sizes of many fixed cutter drillbits present difficult challenges to manufacturability of bit bodieshaving cemented carbides and/or spherical carbides as the matrixmaterials. These same quality problems may occur during manufacture ofother downhole tools firmed at least in part by a matrix of cementedcarbides and spherical carbides such as reamers, underreamers, andcombined reamers/drill bits.

Previous testing and experimentation associated with premixing cementedcarbides and/or spherical carbides with macrocrystalline tungstencarbide and/or cast carbide powders often failed to produce a sound,high quality matrix bit body. increasing soak time of binder materialwithin such mixtures of cemented carbides and/or spherical carbides withmacrocrystalline tungsten carbide and/or cast carbide powders did notsubstantially eliminate quality problems related to shrinkage, alloysegregation, lack of infiltration, porosity and other problemsassociated with unsatisfactory infiltration of cemented carbides and/orspherical carbides. Also, increasing the temperature of hot, liquidhinder material used for infiltration of such mixtures did notsubstantially reduce associated quality problems. Hid alloy segregationin the last solidifying portion of liquid binder material within variousmixtures of cemented carbides and/or spherical carbides withmacrocrystalline tungsten carbide and/or cast carbides was identified asone cause for lack of bonding within such mixtures, undesired shrinkage,porosity and other quality problems.

The use of first matrix material 131 to form a first layer or zone incombination with using second matrix material 132 to form a second layeror zone adjacent to first matrix material 131 may substantially reduceor eliminate alloy segregation in the last solidifying portion of hot,liquid binder material with first matrix material 131. The addition ofsecond matrix material 132 in the annulus formed between outsidediameter 154 of core 150 and inside diameter 37 of metal blank 36 andcovering first matrix material 131 such as shown in FIG. 2 maysubstantially reduce or eliminate problems related to lack ofinfiltration, porosity, shrinkage, cracking and/or segregation of binderconstituents within first matrix material 131. One reason for theseimprovements may be the ease with which hot, liquid binder materialinfiltrates macrocrystalline tungsten carbide and/or cast carbidepowders.

As previously noted, hot, liquid binder material may leach or removesmall quantities of alloys and/or other contaminates from bondingmaterials used to form cemented carbides. The leached alloys and/orother contaminates may have a higher melting point than typical bindermaterials associated with fabrication of matrix drill bits. Therefore,the leached alloys and/or other contaminates may solidify in small gapsor voids formed between adjacent cemented carbide pellets, spheres orother shapes and block further infiltration of hot, liquid bindermaterial between such cemented carbide shapes.

The “contaminated” infiltrant or hot, liquid binder material may havesolidus and liquidus temperatures different from “virgin” bindermaterials. Further “enrichment” of an infiltrant with contaminants maytake place during solidification of the binder material as a result ofrejection of solute contaminants into hot liquid ahead of asolidification front. Besides segregation of contaminants (solute) inlater stages of solidification, any lack of directional solidificationmay give rise to potential problems including, but not limited to,shrinkage, porosity and/or hot tearing.

Macrocrystalline tungsten carbide and cast carbide powders may besubstantially free of alloys or other contaminates associated withbonding materials used to form cemented carbides. The second matrixmaterial may be selected to have less than five percent (5%) alloys orpotential other contaminates. Therefore, infiltration of hot, liquidbinder material through a second matrix material selected in accordancewith teachings of the present disclosure will generally not leachsignificant amounts of alloys or other potential contaminates.

First matrix material 131 may be cemented carbides and/or sphericalcarbides as previously discussed. Alloys of cobalt, iron and/or nickelmay be used to form cemented carbides and/or spherical carbides. Forsome matrix drill hit designs an alloy concentration of approximatelysix percent in the first matrix material may provide optimum results.Alloy concentrations between three percent and six percent and betweenapproximately six percent and fifteen percent may also be satisfactoryfor sonic matrix drill bit designs. However, alloy concentrationsgreater than approximately fifteen percent and alloy concentrations lessthan approximately three percent may result in less than optimumcharacteristics of a resulting matrix bit body.

Second matrix material 132 may be monocrystalline tungsten carbide orcast carbide powders. Examples of such powders include P-90 and P-100which are commercially available from Kennametal, Inc. located inFallon, Nev. Third matrix material 133 may be tungsten powder such asM-70, which is also commercially available from H. C. Stuck, OsramSylvania, and Kennametal. Typical alloy concentrations in second matrixmaterial 132 may be between approximately one percent and two percent.Second matrix materials having an alloy concentration of approximatelyfive percent or greater may result in unsatisfactory operatingcharacteristics for an associated matrix bit body.

A typical infiltration process for casting composite matrix bit body 50may begin by forming mold assembly 100. Gage ring 110 may he threadedonto the top of mold 102. Funnel 120 may be threaded onto the top ofgage ring 110 to extend mold assembly 100 to a desired height to holdpreviously described matrix materials and binder material. Displacementmaterials such as, but not limited to, mold inserts 106, legs 142 and144 and core 150 may then be loaded into mold assembly 100 if notpreviously placed in mold cavity 104. Matrix materials 131, 132. 133 andmetal blank 36 may be loaded into mold assembly 100 as previouslydescribed.

As mold assembly 100 is being filled with matrix materials, a series ofvibration cycles may be induced in mold assembly 100 to assist packingof each layer or zone or matrix materials 131, 132 and 133. Thevibrations help to ensure consistent density of each layer of matrixmaterials 131, 132 and 133 within respective ranges required to achievedesired characteristics for composite matrix hit body 50. Undesiredmixing of matrix materials 131, 132 and 133 should be avoided.

Binder material 160 may be placed on top of layers 132 and 133, metalblank 36 and core 150. In contrast to common practice, no flux layer isused on top of binder material 160. A cover, or lid, 165 may be placedover mold assembly 100. Mold assembly 100 and materials disposed thereinmay he preheated and then placed in a furnace (not expressly shown).When the furnace temperature reaches the melting point of bindermaterial 160, at least a portion (and typically substantially all) ofthe binder material 160 melts and liquefies such that the melted, liquidbinder material 160 may infiltrate matrix materials 131, 132 and 133. Aspreviously noted, second matrix material 132 allows melted, liquidbinder material 160 to more uniformly infiltrate first matrix material131 to avoid, in a subsequent process of solidification, the occurrenceof undesired segregation in the last-solidifying portions of liquidbinder material 160 with first matrix material 131.

Upper portions of mold assembly 100 such as funnel 120 may haveincreased insulation (not expressly shown) as compared with mold 102. Asa result, hot, liquid binder material in lower portions of mold assembly100 will generally start to solidify with first matrix material 131before hot, liquid binder material solidifies with second matrixmaterial 132. The difference in solidification may allow hot, liquidbinder material to “float” or transport alloys and other potentialcontaminates leached from first matrix material 131 into second matrixmaterial 132. Since the hot, liquid matrix material infiltrated throughsecond matrix material 132 prior to infiltrating first matrix material131, alloys and other contaminates transported from first matrixmaterial 131 may not affect quality of resulting matrix bit body 50 asmuch as if the alloys and other contaminates had remained within firstmatrix material 131. Also, the second matrix material preferablycontains less than four percent (4%) of such alloys or contaminates.

Proper infiltration and solidification of binder material 160 with firstmatrix material 131 is particularly important at locations adjacent tofeatures such as nozzle openings 54 and pockets 58. Improved qualitycontrol from enhanced infiltration of binder material 160 into portionsof first matrix material 131 which forms respective blades 52 may allowdesigning thinner blades 52. Blades 52 may also be oriented at moreaggressive cutting angles with greater fluid flow areas formed betweenadjacent blades 52.

For some fixed cutter drill bit designs forming a composite bit bodywith a first matrix material and a second matrix material in accordancewith teachings of the present disclosure may result in as much as fillypercent (50%) improvement in abrasion resistance, one hundred percent(100%) improvement in erosion resistance, fitly percent (50%)improvement in transverse rupture strength and sometimes more than onehundred percent (100%) improvement in impact resistance as compared withthe same design of fixed cutter drill bit having a matrix bit bodyformed with only commercially available macrocrystalline tungstencarbide and/or cast carbide powders, or formulate thereof.

Mold assembly 100 may then be removed from the furnace and cooled at acontrolled rate. Once cooled, mold assembly 100 may be broken away toexpose composite matrix bit body 50 as shown in FIG. 3. Subsequentprocessing according to well-known techniques may be used to producematrix drill bit 20.

As indicated above, in contrast to prior practice, no flux is used ontop of binder 160. It has been common practice in bit manufacturing touse a flux material over the copper binder. Fluxes are used to removegases such as oxygen or hydrogen or prevent their absorption into themelt, to reduce metal loss such as zinc, and/or to remove impurities andnonmetallic inclusions from the melt. Borax (Na₂B₄O₇1OH₂O) and boricacid (H₃BO₃) are considered neutral cover fluxes. Borax melts at 1365°F. and provides a fluid slag cover over the melt. These compounds areused in industry to reduce metal loss (zinc flaring) and to agglomerateand absorb nonmetallic impurities. However, our experience has shownthat contamination of the flux with potassium borates and fluorides ispossible. These compounds are commonly found in other fluxes and havebeen shown to inhibit proper wetting of WC particles by the binderleading to pockets of non-infiltrated loose powder in the bit head. inaddition, numerous inclusions were identified in metallurgical testsections of manufactured bits. A test program was developed to determinethe cause of the metallurgical defects in the bit manufacturing. Thetest program comprised melting an infiltrant binder in a small graphitecrucible and lab furnace under varied furnace atmosphere, flux amount,time at temperature and physical exposure of the molten pool to thefurnace atmosphere.

For each test, approximately 120 g of a copper binder, from BelmontMetals, Inc., Brooklyn, N.Y., was placed in the mold. Either 0 g, 2.4 gor 4.8 g of brazing flux, for example Harris 600 flux, manufactured byHarris Products, Mason, Ohio, constituting 0 wt %, 2 wt % or 4 wt % ofthe binder was added on top of the binder. The samples were placed intoa lab furnace preheated to 2100° F., held at temperature for 10 or 30min, removed and allowed to cool in ambient air. When a nitrogenatmosphere was used in the furnace, no atmosphere monitoring wasperformed. Nitrogen was fed into the furnace at 15 psi and positivepressure was used to inhibit air ingress. At 15 psi, three turns of thechamber atmosphere was estimated to occur in under 2 min, so minimumoxidation should have occurred after insertion of the samples. Theintroduction of nitrogen into the furnace also slowed the temperaturerecovery of the furnace by approximately one hour.

One known qualitative method used to estimate the gas content of a meltis to measure the surface shrinkage or “set” of the sample. All elsebeing equal, samples with a greater amount of sink have a lower gascontent, because less dissolved gas in the melt creates a smallerblowhole upon solidification when the gas is forced out of the metal.Each of the samples were sectioned vertically to determine the relativesize of the blowhole and amount of set, The samples without flux had thesmallest blowholes and greatest amount of set as shown in FIG. 5A. FIG.5A shows a cross sectioned example of a sample 500 manufactured withoutflux as contrasted to a sample 510, see FIG. 5B, manufactured with theflux described above. Sample 500 had 0 % by weight of binder 506, andsample 510 had 2.4% by weight of binder 516. The set 502 of sample 500is significantly larger than the set 512 of sample 510. In addition, theblow cavity 504 of sample 500 is significantly smaller than the blowcavity 514 of sample 510. While presented in 2-dimensional format, it isunderstood that the blow cavities 504 and 514 are 3-dimensional cavitiesenclosed within the solidified samples, 500 and 510, respectively.

Sections from each sample were mourned and polished. Twenty or moreimages for each sample were analyzed, un-etched at 100× magnificationusing image analysis software, for example Simagis brand image software,to determine the section inclusion content. Typical micrographs areshown in FIGS. 6A-6C, where the flux content of the samples, was 0 wt %,2% and 4%, respectively. As can he seen in comparing the micrographs,the inclusions, represented by the size and quantity of dark spots,increase progressively from the 0 wt % flux, to 2 wt % flux, to 4 wt %flux in the samples. These results were unexpected, since commonpractice taught to use flux to reduce impurities in the melt. No attemptwas made to exclude solidification porosity from actual inclusions. Thecooling conditions were similar for all samples so it is assumed theyhave comparable amounts of porosity. Again, the samples with more fluxwere “dirtier” than those with none.

The most prominent inclusion defect was only found in samples with flux.This defect was a boride intermetallic characterized visually by itsopaque color and sharp corners. This intermetallic was foundincreasingly in samples as the flux addition increased and predominatelyinfluenced the inclusion levels identified. Thus, flux is, unexpectedly,directly causing intermetallic inclusion generation in the binder. Athin acicular needle inclusion was often associated with the borideintermetallic. The needle inclusion was too small for energy dispersiveX-ray spectroscopy (EDS) analysis but is believed to also he a boride.Both of these inclusions were also found in the binder head of aproduction hit.

The second inclusion was manganese sulfide (MnS). This small inclusionhas a dark gray color. Historically, higher concentration of this typeof inclusion has been found near the hit surface. It is thought that thesulfur comes from the graphite molds.

Slag samples were taken from at least one flux covered binder testsample and analyzed using the EDS on the SEM. The results were comparedto a similar slag sample removed randomly from a production bit beforemold breakout. Both samples consist predominantly of manganese oxide andsodium oxide with trace amounts of silicon and aluminum oxides. Mn andSi are the most readily oxidized elements in binder while sodium ispresent in borax. (Boron is also likely present in the slag but isusually too light to detect with EDS) Even though the slag containssignificant amounts of manganese, the amount lost to the slag was stillinsignificant to change the chemistry of the binder.

TGA Analysis

Thermogravametric analysis (TGA) was used to establish the onset of hightemperature oxidation of both the binder and graphite. A small TGAsample was removed from a binder cube. In two separate tests, sampleswere heated continuously at 5° C./min or stepwise with 10 min. holdsfrom 400° C. (842° F.) to 850° C. (1562° F.) in air with a purge rate of100 mL/min. In both tests oxidation of the binder started above 900° F.and progressed exponentially as the temperature increase. The oxidationof graphite was also performed because the formation of CO may produce areducing atmosphere inside the mold. A similar stepwise heating cyclewith 10 min. holds from 400° C. (842° F.) to 850° C. (1562° F.) in airwith a purge rate of 100 mL/min was performed on both the funnelgraphite (grade CS) and mold graphite (grade CBY). Both grades startoxidizing around 1100° F. with the funnel graphite oxidizing slightlyfaster than the mold graphite at higher temperatures. Moreover, whencarbon is oxidized at 1000° F., the reactant gas is around 90% CO₂ andonly 10% CO. It is not until temperatures above 1500° F. are reachedthat the gas composition is over 90% CO. This means the graphite attemperatures below 1500° F. is not effective at preventing the oxidationof binder, but at 1700° F., when hinder is liquid and most active, theatmosphere is reducing (protective).

In view of the previous disclosure and unexpected laboratory results,one example of a new fluxless process for manufacturing a matrix drillbit may comprise placing at least a first layer of a first matrixselected from the group consisting of cemented carbides and sphericalcarbides material in a matrix bit body mold; placing a metal blank inthe mold; placing at least a second layer of a second matrix materialselected from the group consisting of microcrystalline tungsten carbideand cast carbide in the mold with the second matrix material operable toimprove infiltration of a hot, liquid binder material throughout thefirst matrix material to minimize incomplete infiltration of the firstmatrix material by the hot, liquid binder material; placing a bindermaterial in the mold with the binder material disposed proximate thesecond layer of matrix material and the metal blank; placing a graphitelid on the mold; heating the mold and the materials disposed therein ina furnace to a selected temperature to allow the binder material tomelt, and to allow the hot, liquid binder material to infiltrate thesecond matrix material and the first matrix material with the secondmatrix material operable to improve infiltration of the first matrixmaterial by the hot, liquid binder material; starting solidification ofthe hot, liquid binder material with the first matrix material beforethe hot, liquid binder material solidifies with the second matrixmaterial; and cooling the mold and the materials disposed therein toform a coherent composite matrix hit body securely engaged with themetal blank.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alternations can he made herein without departing from the spiritand scope of the disclosure as defined by the following claims.

1. A fluxless process for manufacturing a matrix drill bit comprising: placing at least a first layer of a first matrix material in a matrix bit body mold; placing a metal blank in the mold; placing at least a second layer of a second matrix material in the mold; placing a binder material in the mold with the binder material disposed proximate the second layer of matrix material and the metal blank; placing a graphite lid on the mold; heating the mold and the materials disposed therein to a selected temperature to melt the binder material and to allow the melted binder material to infiltrate the second matrix material and the first matrix material, with the second matrix material operable to improve infiltration of the first matrix material by the melted binder material; starting solidification of the hot, liquid binder material with the first matrix material before the hot, liquid binder material solidifies with the second matrix material; and cooling the mold and the materials disposed therein to form a coherent composite matrix bit body securely engaged with the metal blank.
 2. The process of claim 1 wherein the first matrix material is chosen from the group consisting, of: a cemented carbide material and a spherical carbide material.
 3. The process of claim 1 wherein the second matrix material is chosen from the group consisting of a microcrystalline tungsten carbide material and a cast carbide material.
 4. The process of claim 1 wherein the second matrix material is operable to improve infiltration of the hot, liquid hinder material throughout the first matrix material to minimize incomplete infiltration of the first matrix material by the hot, liquid binder material.
 5. A process for reducing inclusions during manufacturing of a matrix drill bit comprising: placing at least a first layer of a first matrix material in a matrix bit body mold; placing a metal blank in the mold; placing at least a second layer of a second matrix material in the mold; placing a binder material in the mold with the binder material disposed proximate the second layer of matrix material and the metal blank: placing a graphite lid on the mold; heating the mold and the materials disposed therein to a selected temperature to cause the binder material to melt and to allow the hot, liquid binder material to infiltrate the second matrix material and the first matrix material, with the second matrix material operable to improve infiltration of the first matrix material by the hot, liquid binder material without using a flux material; starting solidification of the hot, liquid binder material with the first matrix material before the hot, liquid binder material solidifies with the second matrix material; and cooling the mold and the materials disposed therein to form a coherent composite matrix bit body securely engaged with the metal blank.
 6. The process of claim 5 wherein the first matrix material is chosen from the group consisting of: a cemented carbide material and a spherical carbide material.
 7. The process of claim 5 wherein the second matrix material is chosen from the group consisting of a microcrystalline tungsten carbide material and a cast carbide material.
 8. The process of claim 5 wherein the second matrix material is operable to improve infiltration of the hot, liquid binder material throughout the first matrix material to minimize incomplete infiltration of the first matrix material by the hot, liquid binder material. 